How the Brain Processes Important Information

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Scientists at UT Southwestern Medical Center have gained fresh insights into how the neurotransmitter dopamine, which is used by nerve cells to communicate with one another, helps brain cells to process important information.

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Studying cells in mice, the researchers have found that this neurotransmitter causes certain brain cells to become more flexible, and changes brain-cell circuitry to process important information differently than mundane information.

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"This can help one remember a new, important episode as distinct from any other episode, such as remembering where you parked your car today versus yesterday," said Dr. Robert Greene, professor of psychiatry at UT Southwestern.

"If we can one day manipulate the way that salient information is processed, we might be able to not only improve learning, but also improve the learning needed to extinguish severe fear responsiveness, such as when a soldier can't forget emotional war memories associated with post-traumatic stress disorder," he said.

Given that conditions like addictions and schizophrenia are associated with alterations in dopamine in the brain, the researchers believe that their findings may one day prove helpful in dealing with them.

It is known that dopamine is released in the brain in association with experiencing "important" events and remembering salient acts, such as learning to avoid a hot stove or that a good grade is rewarded.

Dr. Greene said that the current study focused on how dopamine operates on the cells associated with this type of memory formation.

He and his colleagues isolated slices of the hippocampus region of the animals' brains, and electrically stimulated the cells.

To simulate what happens in the brain in response to a memory-worthy event, they then exposed the cells to a selective dopamine-like neurotransmitter agent and repeated the stimulation.

When the researchers compared the effects of the stimulation with and without the dopamine agent, they identified changes in the responses of NMDA receptors, proteins that mediate synaptic plasticity when activated.

"The NMDA responses changed to increase the cells' plasticity, and we think that this facilitates learning and memory," Dr. Greene said.

Besides that, according to the researchers, the changes in NMDA responses to dopamine agents changed the functional circuitry of the cells, making the cells more responsive to electrical impulses coming from an indirect route through three processing "stations" before they reached the output region of the hippocampus.

Dr. Greene said that in the absence of dopamine, the cells tend to respond instead to impulses travelling by a route that is more direct and requires less processing.

Information sent by this direct route may reflect what is already known, and is less likely to change the animal's behaviour.

"You don't want to have interference from yesterday. You need to know where you parked your car today, and dopamine may help to ensure that information from today will be remembered as distinct from yesterday," he added.

He and his colleagues will net study how dopamine modulation affects learning and memory-related behaviour, and exactly how dopamine acts on cells and their circuits.

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